By way of introduction, watermarking may be used to detect illegally distributed content and to determine the origin of the illegal distribution.
The following references are believed to represent the state of the art:    US Published Patent Application 2006/0048633 of Hoguchi;    US Published Patent Application 2006/0239501 of Petrovic, et al.;    Japanese Published Patent Application 2005 049409 of University of Meiji; and    Korean Published Patent Application 2009 0093530 of University of Seoul Industry Cooperation Foundation.